Conductive ink



Patented Dec. 9, 1941 CONDUCTIVE INK Samuel Brand, Otto Weitmann, and Kenneth J.

Mackenzie, Binghamton, N. Y., assignors to International Business Machines Corporation, New York, N. Y., a corporation of New York No Drawing. Application March 12, 1941, Serial No. 382,934

3 Claims.

This invention relates to conductive ink, particularly, one which, when applied to suitable carrying mediums, can be used for conducting electricity along the characters formed upon the mediums. The present application is a continuation-in-part of the copending application Serial No. 312,378, filed January 4, 1940.

For accounting systems, it has been suggested, to form legible or graphic characters upon control sheets to indicate the desired data, and in addition thereto, to form or print the said characters by employing electrically conductive inks. The characters thus formed are adapted to be sensed by electrical members, which permit current to flow when a significant portion of the character outline appears in the area traversed by the sensing members: thus, it is seen that the characters, formed by the conductive ink, when sensed, are utilized for closing electrical circuits for controlling particular control elements of the accounting machines employed in such systems.

It is well known in many instances, that the same control sheets are used repeatedly in the machines -for various control purposes, and that the physical requirements of the control sheets must be such as to withstand the stresses to which they are subjected by the rapid and repeated handling of the sheets in the diflerent accounting machines, and therefore, must be capable of withstanding the exigencies of such repeated operations. Now, it will be understood, that the characters which are formed with the conductive ink on the control sheets are also subjected to continuous stresses by virtue of the engagement of the electrical sensing members with the electrically conductive characters.

It has been found when the printed characters on the control sheets are formed by using the known conductive inks, and subjected to repeated sensing operations, that the outlines of such characters are mutilated or worn away, consequently resulting in having deformed characters remaining on the sheets whose outlines or configurations are no longer continuous or whole. It is obvious that under such conditions faulty sensing operations and faulty operations are effected as a result of the mutilated characters; thus, it is of extreme importance to form the characters by a conductive ink, which is capable of withstanding the exigencies of such repeated sensing operations to insure accurate sensing operation and consequently accurate operations of the machines.

It is, therefore, an object of the present invention to provide a conductive ink which is suitable for forming electrically conductive characters on suitable carrying mediums, such as control sheets, and one which overcomes the defects outlined hereinabove; and more particularly a conductive ink for forming electrically conductive characters on a sheet, which characters, when sensed, are capable of withstanding the exigencies of repeated sensing operations in accounting machines.

Another object of the invention is to produce an electrically conductive ink which is suitable for application upon a transfer medium, such as a suitable ribbon, tape, or sheet, and capable of being transferred from the said medium to a control sheet by a blow exerted by an indicia or type member, under manual or automatic control, to produce on the sheet a deposit or character mark which is homogeneous throughout and electrically conductive.

Applicants are cognizant oi the fact that conductive inks generally are well known and have been suggested for some of the purposes outlined hereinabove. Examples of such conductive inks are found in the U. S. Patents Nos. 1,034,103, 1,034,104, and 2,084,849. It has been found, however, that such inks are unsuitable to attain the purposes of this invention.

The conductive ink comprising the present invention has been found to be of the type, which, when applied to a suitable control sheet, leaves a deposit which is homogeneous throughout and electrically conductive, so that the outlines of the characters formed by such deposits, when applied directly to the sheet or by means of a transfer medium, can be traversed innumerable times by suitable sensing members without altering or mutilatlng the homogeneity of the character outlines. It is preferred to provide an ink oi the character described, for the above described purposes, which is more viscous than the well known fluid inks, and particularly those fluid inks of the recuperative type. It has been noted that with other types 01' known inks, particularly when used with transfer mediums, that nonhomogeneous portions or sections of the character outlines are produced. Such faulty i'ormatlons of the character outlines are partially due to the improper density of the conductive inks.

It should be understood that the conductive ink suitable for the above purposes must have suiflcient mass and body which, when deposited, not only adheres properly to the sheet but one which also forms a homogeneous deposit capable of withstanding the exigencies of repeated sensins operations. Suitable tests have shown that the character outlines formed by applicants conductive ink, by using a transfer medium for transferring the ink, are capable of withstanding in excess of 25,000 repeated sensing operations without affecting the electrical conductivity characteristics of the character outlines.

In addition to the advantages lust set forth, it is to be noted that the deposits of applicants conductive ink on the control sheets dry readily and quickly, so that smudging or blurring of the characters formed on the sheets is overcome; also. when the same conductive mk is applied to the transfer mediums it has been found that sufflclent fluidity is contained by the ink for rendering the transfer mediums usable for comparatively long periods of time. An additional feature of the present type of ink is its density as compared with the inks of the prior art, which renders it extremely suitable for forming characters which are to be sensed or read by machines utilizing rays of radiant energy as the sensing medium.

Other objects and details of the invention will be understood and apparent from the following description, wherein for purposes of illustration an example of a preferred embodiment of the invention is set forth.

It has been found that a conductive ink of the character described can be produced by combining a conductive ingredient, such as graphite, or the like, with a suitable inorganic filler such as kaolin, bentonite, etc., a plasticizer comprising a hygroscopic polyhydric alcohol such as glycerine, sorbitol, etc., and a suitable highly volatile solvent, which is miscible with the plasticizer, comprising, for example, a monohydrlc alcohol, such as ethyl alcohol, Solox, etc. Solox" is an example of one suitable type of denatured ethyl alcohol.

The conductive medium may, if desired, be in colloidal form which, for example, can be a colloidal graphite known as Acheson defloculated graphite; however, it has been found that the graphite particles need not be ground to such a degree of fineness, instead, a graphite can be used,

the size of the particles of which are of such a degree of fineness that the average size is approximately Z A microns. An example of a suitable graphite other than the said colloidal graphite is the Dixon micronized graphite.

In view of the foregoing, it should be evident that certain specific requirements are required of the conductive ink to be used for the purposes described hereinabove. Obviously, in the case of ribbons coated with the conductive ink, the latter must adhere readily to the ribbon, but also must be capable of transferring readily, for example, by means of the pressure exerted by type bars of standard typewriting or printing machines. The outlines of the transferred characters must remain homogeneous.

The inorganic filler ingredient in the conductive ink aids in giving it more body, so that the admixture attained is a more homogeneous mass. The plasticizer renders the mass more pliable, and due to its hygroscopic characteristic maintains the desired consistency of the admixture, and also prevents the prepared ribbon from drying out too much at low humidities. With respect to the consistency of the admixture retained by the ribbon, it should be stated that it must be a firm but pliable mass. Obviously, after the application of the coating of ink to the ribbon, the solvent evaporates to leave the deposit of the graphite, filler, and plasticizer ingredients on the ribbon. For this reason, the percentages of the amounts of the solvent used in the ink admixture are not critical. The type of coating process employed for coating the ribbons will determine the desired consistency oi the coating mixture. In applicants coating process, the mixture preferred is highly viscous, and can properly be described as a soft paste.

It has been determined, by experiment, that the operative features of the described ink, depend malnly on the ratios of the conductive and filler ingredients. The ratios of the plastlcizer and the solvent are not critical, in view of the statements just set forth. The range of the ratios of the different ingredients is indicated in the following table:

I Plssticizerflnivent ififlfligl litltve ff solution comprisngre1e nng glycerlne graphite ggfig 62.5% and alcohol Gm ma Gm me (a All of the conductive inks when applied to ribbons have been found to produce the desired results outlined hereinabove. Bentonite is a suitable filler for the above mentioned inks and can be used in place of kaolin. It is noted that the ratios of the conductive ingredient to the inorganic filler ingredient range from approximately 83% to 17% and 42% to 58%, respectively. Thus, it is seen that the amount of the conductive ingredient in the mixture of the conductive-inorganic filler ingredients may be greater than 42% and not less than 83% of the whole.

Thus, it is seen that in addition to the conductive ink specifically set forth in the said copending application, suitable inks can be formed by varying the ratios of the ingredients within certain defined limits. This said ink referred to comprises the following combination of the ingredients: approximately 7.5 grams kaolin, 12.5 grams graphite (approximately 2 micronsfineness) 25 c. c. glycerine, and 15 c. c. alcohol.

Another suitable ink, using a different type of plasticizer, comprises the following: 7.5 grams kaolin, 12.5 grams of the said graphite, 26 c. c of an 83% solution of sorbitol, and 15 c. c. of alcohol.

While there has been shown and described and pointed out the fundamental novel features of the invention as applied to a single modification, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention. It is the intention therefore to be limited only as indicated by the scope of the following claims.

What is claimed is:

l. A conductive ink of the character described comprising approximately 7.5 grams kaolin, 12.5 grams graphite, the average particle size of which is approximately 2 microns, 25 c. c. glycerine, and 15 c. c. alcohol.

2. A conductive ink of the character described comprising a highly viscous paste formed of graphite, the average particle size of which is approximately 2 /2 microns, an inorganic filler,

wherein the amount of graphite in the graphite filler admixture is greater. than 42% and less than 83%, a plasticizer comprising approximately 35 to 45 c. c. 0! a hygroscopic polyhydric alcohol,

and a highly volatile solvent which is miscible wherein the amount of graphite in the graphite filler admixture is greater than 42% and less than 83%, a plasticizer comprising an hygroscopic polyhydric alcohol, and a highly volatile solvent which is miscible with the plasticizer.

SAMUEL BRAND. O'I'IO WEITMAN KENNETH J. MACKENZIE. 

